The present invention relates to a device for detecting electromagnetic stray effects.
Four rpm sensors, which are assigned to the respective wheels, are customarily employed in connection with vehicles equipped with an anti-lock system (ABS) or a traction control system (ASR), (ABSR), or a dynamic drive control (FDR). Customarily the rpm sensors are inductive pick-ups, whose output signal shows a sinusoidal progression. Following processing, a triangular-shaped pulse sequence is obtained, the rpm of the respective wheel can be determined from the chronological distance of the individual pulses or individual pulse flanks.
The information derived from the rpm sensors is supplied to a control unit, for example an ABS control unit, which performs the required control steps on the basis of the detected wheel rpm. Since erroneous output signals of the rpm sensors negatively affect the control, it should be assured that the signals supplied ru by the rpm sensors are actually based on the rpm of the wheel and not on possible stray signals. Inductive rpm sensors react particularly sensitively to exterior influences, for example field changes caused by public electrical power nets which are known to have frequencies of 50 or 60 Hz. It is possible to generate signals by means of such electrical power nets in the rpm sensors, which do not correspond to the control value to be detected, i.e. not to the rpm to be detected. Such signals are called stray effects.
Electromagnetic stray effects not only occur with rpm sensors, but also with inductive sensors in general, for example with sensors for distance measuring, angular changes, for example in engine control, etc. When used in vehicles in particular, steps should be taken to detect the stray effects and make it impossible for signals, which are generated by inductive stray effects, to be erroneously used as useful signals.
An anti-lock system, wherein a detection of stray effects caused by electromagnetic fields of the electrical power nets on inductive receivers is performed, and wherein the anti-lock system itself takes steps which assure that no undesired control conditions occur because of the stray effects, is known from patent application DE-P 1 95 032 71.3. In this known anti-lock system, the vehicle reference velocity required for control is determined from output signals of wheel rpm sensors. As soon as it is noted that the frequency of the signal to be evaluated lies within a critical range of approximately 50 to 60 Hz, additional steps are taken which prevent that stray effects result in errors in the calculation of the reference velocity.
The signals generated by electromagnetic stray effects from electrical power nets disadvantageously arise in particular if no signal at all should be generated by the rpm sensor, i.e. when the vehicle is stationary or moves in a speed range below 2.75 km/h. The stray effect signals at frequencies of 50 or 60 Hz cause some problems in particular in connection with presently used braking control units at speeds of approximately 5 to 15 km/h. Which speed is particularly critical is a function of various parameters, for example the wheel circumference, the number of teeth of the disk scanned by the sensor, etc. The amplitude of the electromagnetic stray effects customarily lies below 150 mV. At frequencies of 50 to 60 Hz, the signals from the rpm sensors should lie in the Volt range. Based on these facts, known per se, the object of the invention is to dependably detect electromagnetic stray effects in the range of 50 to 60 Hz, which for example are caused by the public electric power nets, and to assuredly suppress the associated information before it is supplied to a downstream located control device, or to compensate them. This object is attained by a device for the detection of electromagnetic stray effects.